Trunked systems in communication networks are well known. Trunked systems allow for efficient use of available bandwidth by multiple users of the network, whereby multiple conversations can be carried over only a few distinct frequencies. Trunked systems are used by many private and government entities using special purpose spectrum allocated to a city, county, public or other dedicated purposes to provide two-way communication for many types of field operations such as construction, fleet operations, fire department deployment, police response and other municipal services.
A trunked radio communications system allows for sharing of relatively few radio frequency channels among a large group of users. When any user in a group wishes to converse with another user, a vacant radio channel assigned to the group is found automatically by the system and the conversation takes place over that open channel. In this manner, multiple unrelated conversations can occur on a single channel, making use of the otherwise idle time between conversations. A control channel is used to coordinate all the communication traffic from the radios on the network. The control channel computer directs packets of data to enable one user group to talk together, regardless of frequency.
There are a number standardized wireless signal packet and modulation protocols and techniques for facilitating communications when there are a large number of system users using a particular trunked network. Such protocols include code division multiple access (CDMA), time division multiple access (TDMA) and frequency division multiple access (FDMA). In these systems, communications between users are conducted through one or more base stations. A first user on one remote device communicates to a second user on a second remote device by transmitting data on the reverse link to a base station. The base station receives the data and can route the data to another base station. The data is transmitted on the forward link of the same base station, or a second base station, to the second remote device. The forward link refers to transmission from the base station to a remote device and the reverse link refers to transmission from the remote device to a base station. In IS-95 systems, the forward link and the reverse link are allocated separate frequencies.
The remote device communicates with at least one base station during a communication. CDMA remote devices are capable of communicating with multiple base stations simultaneously during soft handoff. Soft handoff is the process of establishing a link with a new base station before breaking the link with the previous base station. Soft handoff minimizes the probability of dropped calls. A method and system for providing a communication with a remote station through more than one base station during the soft handoff process are disclosed in U.S. Pat. No. 5,267,261, entitled “MOBILE ASSISTED SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM”.
Within current communication networks, there are a number of significant difference between the transmission of voice and data. For an acceptable user experience, voice transmissions require a fixed and common quality of service for all users. Typically, for digital systems providing voice services, this translates into a fixed and equal data transmission rate for all users and a maximum tolerance value for the error rates of the speech frames, independent of the link resource. For the same data rate, a higher allocation of resource is required for users having weaker links. This results in an inefficient use of the available resource. In contrast, for data services, the quality of service can be different from user to user and can be a parameter optimized to increase the overall efficiency transmission within the data communication system. The grade of service for a data communication system is typically defined as the total delay incurred in the transfer of a data message.
Another significant difference between voice services and data services is the fact that the voice imposes stringent and fixed delay requirements. Typically, the overall one-way delay of speech frames must be less than 100 msec. In contrast, the data delay can become a variable parameter used to optimize the efficiency of the data communication system based on the required quality of service. Additionally, the configuration of voice and data transmitted across the network may be significantly different. Most industry standard internet and communication protocols are too cumbersome to use on narrow band data links. They are also complex, for example TCP/W, X.25 or HDLC requires specialized hardware to implement, and again, for the simple micro-controller, the software development required is excessive. Further, current wireless data systems generally require significant wideband capacity to support the extensive voice and data requirements of user. Wideband is also required to provide the control channel functions for tracking and logging activity on user devices. This need for wideband capacity has resulted in a complex network with expensive infrastructure and airtime costs.
In the United States radio communication is regulated by the Federal Communication Commission under its FCC Rules Title 47 Code of Federal Regulations and related rules including FCC Part 22, 15 and 101.
A relatively low-cost communication system designed to use simple micro-controller based devices and optimized for narrow band transmission of voice and data services over narrow-band networks is needed. The present invention provides a channel structure and protocol which facilitate transmissions of data and voice services. Given the growing demand for wireless data applications and the constraints on wireless bandwidth capacity, the need for very efficient wireless data communication systems has become increasingly significant. What is needed is a novel and improved narrowband channel structure and protocol for use in wireless data communication systems.